The cooling systems of liquid-cooled, internal combustion engines in vehicles are usually closed positive-pressure systems and include as a component a surge tank. The surge tank fulfills several important tasks: it must compensate for the volume changes resulting from the temperature changes of the cooling liquid, it must collect the air present in the liquid system, and it must prevent excessive depression or cavitation in front of the coolant pump. The surge tanks are typically installed in parallel with the main liquid circuit between the radiator and cooling passages formed in the engine block and cylinder head. The surge tank is so connected that the deaeration line, starting from the highest geodetic point of the cooling system, discharges generally upward into the surge tank and the fill line from the surge tank is connected proximate the pump intake of the liquid coolant pump.
The engine is mounted in a vehicle chassis. The cooling system radiator is mounted in proximity to the engine and at relatively the same level. A cooling system surge tank is mounted high on the firewall of the vehicle, above the level of the engine and radiator. A vent or deaeration line is connected from a point on the engine just below the coolant thermostat up to the bottom of the surge tank. A second larger conduit is connected also from the bottom of the surge tank to the engine near the water pump inlet. The purpose of the surge tank, which is part of the pressurized cooling system is:
(1) To allow the operator to check the level of coolant in the system. PA1 (2) To allow expansion and contraction of the coolant, while always maintaining the coolant level in the radiator and engine at 100% full. PA1 (3) To allow, by means of the deaeration line described above, the venting of any entrapped air in the engine and radiator as the system is initially filled with coolant. Should any air be drawn in for any reason after the initial fill, the air will find its way to the high point of the engine and be expelled through the deaeration line to the surge tank. PA1 (1) After initial build of the vehicle, when the coolant is installed by the fast fill method the deaeration line is of a size that easily allows the expulsion of large amounts of air. The line is initially of the same diameter as is currently employed. PA1 (2) Once the engine is started and begins to generate heat, the coolant warms up, and the heat shrink material used for the deaeration line causes the deaeration line to reduce its inside diameter (decreasing the cross-sectional area of the fluid passageway) and thereby to reduce the coolant flow through the deaeration line, causing an increase in the performance of the cooling system. PA1 (3) No components other than the deaeration line conduit need be changed. All connections made at the engine and surge tank remain the same. No machining of the engine components and/or surge tank is affected. PA1 forming the conduit of a heat responsive material; PA1 flowing a fluid through the conduit; PA1 running the engine to an elevated fluid temperature; and PA1 contracting the conduit fluid passageway responsive to the heating of the conduit caused by the fluid flow therein.
It should be noted that the deaeration line always remains open. It is not throttled by the cooling system thermostat or any other regulating device. Therefore, there is always the possibility of coolant flow from the engine through the deaeration line to the surge tank. This depletion of the coolant from the engine is returned via the second connection from the surge tank (the fill line) to the area of the water pump inlet on the engine.
While this constant flow to the surge tank and back to the engine serves to purge any entrapped air to the surge tank, it is not beneficial to the performance of the heat exchange function of the cooling system. As compared to the cooling system radiator, the surge tank serves as a poor heat transfer component. Ideally, the deaeration line would be sized as small in diameter as might be possible, still allowing air to escape upwards to the surge tank, but small enough to greatly restrict the flow of coolant to the surge tank in normal operation. The ideal is to purge air from the coolant, but to greatly limit liquid flow to the surge tank so that as much of the total volume of coolant is available for the radiator to efficiently perform the coolant cooling function.
Typically, the deaeration line is sized to provide an inside diameter that will allow the air to be evacuated from the engine and radiator when the pressurized fast fill system of pumping coolant into the system at the original build site (factory) is incorporated. The fast fill system requires substantially greater flow rates through the deaeration line than is required during normal engine operation. This fast fill system is used to reduce coolant fill time and the labor associated with it. Once in normal service, a vehicle would not again be subjected to this fast fill coolant method, even at a dealership. Therefore, the deaeration line which was sized to allow a great volume of air to be expelled during fast coolant fill, is not called on again to perform its function at such a high volumetric rate for the remainder of the vehicle life. In normal operation, any mass flow of coolant through the deaeration line is detrimental to the total cooling system performance. Accordingly, there is a need in the industry to be able to use the fast fill system at engine build and, in normal engine operation, to purge air from the coolant, but to greatly limit liquid flow to the surge tank during normal engine operation so that as much of the total volume of coolant as possible is available for the radiator to efficiently perform the coolant cooling function.